HTDELETE

This wait type (and the other HT* waits) is when a thread is waiting for access to the shared hash table used during batch-mode processing. SQL Server 2012 used to use a hash table per thread and SQL Server 2014 now uses a shared hash table. This change was made to reduce the amount of memory required for the hash table, but comes at the expense of these waits when synchronizing access to the hash table. Typically these waits occur when queries involve columnstore indexes, but they can also occur without columnstore indexes being involved if a hash operator runs in batch mode.